SE455890B - KEEP DETERMINING THE BODY OF A SOUND CELL WITHIN A WATER AREA AND PLANT FOR EXECUTING THE KIT - Google Patents

Description

455 890 2 only have a limited range, whereby the interception devices can furthermore be of a simple and inexpensive design.

In order to quickly get a water area under surveillance, the interception devices can be deployed by aircraft or helicopters. It is then suitable to let the listening devices occupy arbitrary, previously unknown positions, eg float around freely, whereby according to another feature of the invention the position of each listening device is determined using the difference in running time for radio waves to at least three radio stations with known positions.

A plant for carrying out the method is characterized according to the invention in that a number of intercepting devices are spread out with an unknown position within the water area, suitably attached to free-floating buoys, that each intercepting device in addition to hydrophone and transmitter is also provided with selective control receivers. and that the system includes at least three radio stations with known positions with receiving means for receiving modulated signals from selected listening devices, and there are first correlating means for comparing the time state of a signal from a selected listening device received in the three radio stations and second correlator means for comparing the time state of a signal representing sound emitted from the sound source and recorded by at least three selected listening devices, and evaluation means for determining the position of each selected listening device by means of the output signal from said first correlator means using determining the running time of the radio waves from the respective listening device to the three radio stations and determining the position of the sound source relative to the selected listening devices by means of the output signal from said second correlator means using the running time of the sound waves from the sound source to the selected listening devices.

The control of the interception devices may, for example, consist of a control command for activating or deactivating the transmitter part so that the interception device starts transmitting or interrupts the transmission of audio information. Furthermore, the control can refer to orders for channels to be used in the transmission. In this way, each selected listening device can be given its own channel. In a plant where the intercepting devices are placed in arbitrary, unknown positions, eg floating freely in the water area, there must be at least three fixed radio stations with known positions, which radio stations are provided with means for receiving a characteristic signal from each selected intercepting device, means for determining the position of each listening device by comparing the time position of said characteristic signal when it is received in the three fixed radio stations.

The characteristic signal may be the recorded audio information, but this signal is due to its low frequency character less suitable for locating the listening devices 455 890. In a preferred embodiment, the characteristic signal is a special signal which is transmitted intermittently at regular intervals during short interruptions in the sound-modulated carrier. In order to simultaneously identify the different eavesdropping devices, the special signal may suitably contain an individual identification information, so-called ID information, for each eavesdropping device.

In principle, the mutual time mode of the different signals can be determined by means of accurate or synchronized clocks in the different stations. Each station could then determine the time state of a given signal, whereby the final position determination then takes place by comparing these stored values. An advantage, however, is if the signal processing can largely take place in real time without the use of synchronized clocks or the like. A system where this is possible is characterized in that at least two of the radio stations with known position are relay stations which relay the modulated signal from each selected listening device to a master station, where time correlation between the different signals from one and the same listening device takes place with knowledge. about the known running times from the respective relay station to the master station.

The invention is illustrated in the accompanying drawings, in which Fig. 1 shows a schematic overview view of a monitoring system operating in accordance with the principles of the invention comprising a large number of free-floating eavesdropping devices and three fixed radio stations, one of which is a master station and the other two relay stations; block diagram for an embodiment of a listening device in a plant according to Fig. 1, jig_§ shows a simplified block diagram of the signal processing part in the master station, which relates to determination of the position of a sound source relative to three selected listening devices, Fig. 1 shows a simplified block diagram of the signal processing part which relates to the determination of the position of a selected listening device, and Figs. shows a simplified block diagram of a listening device operating with digitized audio signal and channel separation achieved by time division multiplexing. The monitoring system according to Fig. 1 comprises a number of spaced apart listening devices A1, A2 ... An, which together cover a water area to be monitored with respect to any sound sources. Such a sound source is shown at U. The distance between the interception devices is adapted to the circumstances and can, for example, within an area of archipelago nature amount to approximately 5 km. The interception devices are assumed to be supported by floating buoys floating in the water.

Each listening device comprises a hydrophone and a transmitter / receiver with an associated antenna. The interception devices are individualized by a special identification address (ID address). An embodiment of a listening device is described in connection with Fig. 2. 455 890 According to Fig. 1, the monitoring system also includes at least three fixed radio stations M1, M2 and M3, of which M1 is a master station and M2 and M3 are relay stations. The radio stations can be stationary facilities but alternatively mobile in the sense that they can be set up in different places in connection with a water area to be monitored. During each measurement, the radio stations have fixed and known positions. The master station has transmitters / receivers for transmitting control information to the listening devices and for receiving information signals from these devices as well as from the relay stations.

The master station also includes signal processing circuits for performing certain signal processing in real time. Via radio link or in another way, the master station can be connected to an evaluation center EC, where final signal processing and position determination takes place. The relay stations M2, M3 also contain transmitters / receivers and are designed to receive certain signals from the listening devices and transmit them to the master station in other radio channels. 1 The position adjustment is in principle carried out in the following way.

It is assumed that only the listening devices A1, A2 and A3 which are best placed for position determination of the sound source U are active. These listening devices simultaneously and individually transmit the recorded sound on a carrier to the master station. In the master station, the radio waves are demodulated and the resulting sound waves are correlated in pairs. Each correlation gives a time difference that represents a given hyperbola. The sound source is located at the intersection of the two hyperbolas thus obtained. (At certain time differences, two intersection points are theoretically obtained, of which, however, one can be excluded). This position determination ignores the difference in the running time of the different radio waves because the running time of the sound waves in the water is considerably greater than the running time of the radio waves.

At regular intervals, each eavesdropping device interrupts its transmission of sound waves and instead transmits its ID address on a separate radio channel. These ID addresses are further relayed by the relay stations M2 and M3 in new radio channels. It is assumed that at a certain point in time only one eavesdropping device, eg A1, transmits its ID address. The master station then receives this ID address directly in a radio channel, ”partly the same address via M2 in another channel and via M3 in a third channel. Since stations M1, M2 and M3 have known positions, the travel times between M2 and M1 (= fl) and between M3 and M1 (= Zê) are also known. By correlating the ID signal obtained directly from A1 with the one received via M2 with compensation for the known running time / fl, a time difference is obtained which represents a hyperbola. By correspondingly correlating the ID signal obtained directly from A1 with that obtained via M3 with compensation for the known running time (2, a time difference is obtained which represents a second hyperbola. At the intersection of these hyperlinks is then A1. The intercept devices A2 and A3 are located in the same way during the intervals at which they transmit ID signal.

Now that the position of the sound source U is determined relative to the listening devices A1, A2, A3 and the position of each of these devices is determined, full information has also been obtained about the absolute position of the sound source U.

In order to clarify the process, a summary of the various signals that appear in the system follows, whereby the specified bandwidths and modulation types apply to an embodiment described in the following.

Signal no. 1 Task: Route: Basic type: Spectrum: Modulation: Signal no. 2 Task: Route: Basic type: Spectrum: Modulation: åmf fl ië Task: Route: Basic type: Spectrum: Modulation: Remark: Signal no. 4 Task: Route: Basic type: Spectrum: Modulation: Transmit the sound of the measuring object to listening buoys.

Measuring objects for at least three selected buoys.

Sound waves in water. 10 Hz or lower to 1000 Hz.

Missing. No carrier.

Enable positional alignment of measuring objects relative to the selected buoys.

'From the buoys to a radio receiver ashore.

Radio waves. Modulated carrier (eg 300 MHz).

The order of magnitude 10 kHz.

Subcarrier, one for each buoy, modulated with signal 1 on a main carrier.

Enable positional adjustment of buoy.

From the current buoy to at least three radio receivers ashore.

Radiovâgor. Modulated carrier (eg 300 MHz). for example 1 - 10 MHz.

Pulse modulated key signal.

One of the land stations can be designated as a master, whereby the signals of the other three receivers are relayed to this master.

Buoy-selective command; Activation and channel selection.

From a land station to a buoy (one at a time).

Radio waves. Modulated carrier (300 MHz).

Depending on the desired command speed: e.g. 10 kHz at moderate command speed.

Pulse modulated key signal. 455 890 Signal no. Task: Surface-selective activation.

Route: From three land stations to all buoys within the area specified by the signal.

Basic type: Radio waves. Modulated carrier (eg 300 MHz).

Spectrum: Depending on the desired accuracy in the surface selection; for example 1 - 10 MHz.

Modulation: Pulse modulation.

As can be seen from the above table, only the signals 3 and 5 are broadband; all other signals have a narrow spectrum (= bandwidth). Signal no. 5 which relates to surface-selective activation of the buoys, i.e. activation of all buoys within a selected surface, has been included for the sake of completeness in the above arrangement but will not be discussed further in this description. Regarding signal no. 5 is referred to .SE B 4351978 where an example of such a surface-selective activation is described.

Fig. 2 schematically shows the construction of an embodiment of a listening device in the form of a buoy which is intended to be placed freely floating within a water area to be monitored. The buoy consists of an antenna 10, which by means of a floating body 10a is kept floating in the water surface, and a buoy body 11 whose connecting cable has such a length and whose specific weight is such that it lies at a suitable depth below the water surface. At the bottom, the buoy is equipped with a hydrophone 12 for sensing sound waves or pressure waves in the water.

The body 11 contains electrical circuits included in the listening device which comprise, among other things, a transmitter / receiver unit 13 connected to the antenna. This unit is illustrated in the drawing as containing a receiver 14 and two separate transmitters 15 and 16. The transmitter 15 is designed to send identification information to the master station and has an input connected to a memory 17 via a switch 18 and a scanner 19. The memory contains an ID number which is unique to each listening device, which information is sensed and converted into serial form by the scanner 19. The transmitter 16 is designed to transmit busy sound and has an input connected to the hydrophone 12 via a switch 20 and a signal converter Z1. The switches 18 and 20 are switched in synchronism between a first position I, where the switch 20 is closed and the switch 18 is open, and a second position II, where the switch 18 is closed and 20 is open. The switches are switched from a clock 22 via a drive stage 23. The timing can be such that the switches are normally in position I and only briefly with Ii. 455,890 even intervals are adjusted in position II, eg position II takes less than 10 msec every ten sec. The clocks can run slightly differently on the different buoys to prevent several devices from sending ID information simultaneously for a longer period of time.

The information transmission via the transmitters 15, 16 takes place by modulating an HF carrier, whereby the transmitter 16 can transmit in several different channels while the transmitter 15 has its own channel. The channel used in 16 is determined by a control signal on a control input 24. In reality, two separate transmitters do not have to be arranged but a common transmitter can be used, 15 being represented by a given channel in this transmitter. The channel separation can be achieved by each channel having its own carrier or its own subcarrier on a common HF carrier.

The receiver 14 also connected to the antenna 9 is designed to receive control information and has an output connected to a register 25 via a detector 26. The control information may be in the form of a pulse train of HF pulses representing a digital message, the register 25 may have the form of a shift register where this message is entered and stored. As an example of how such a message can be composed, Figure 2 shows a register 25 consisting of a number of sections. In a first section 27, a series of numbers is stored which represents the ID number of the interception device you want to control. This section of the shift register is connected to a comparator 31 which at a second input receives information from the ID memory 17. In another section 28 a number representing orders for activation is stored and in a section 29 a figure representing deactivation order. Finally, a section 30 stores a number representing the channel to be used. The output of the comparator 31 is connected to one input of an AND gate 32 having a second input connected to the section 28 of the shift register 25. The output of the comparator 31 also leads to one input of an AND gate 33 having a second input connected to section 29 of the register 25. The output of the AND gate 32 leads to a changeover control input of a controllable switch 34 and the output of the AND gate 33 leads to a reset control input of the same switch. When a signal is received from the AND gate 32, the switch 34 closes and provides a connection between a current source 35 and a block 36 representing the elements of the transmitter part which require driving voltage. The transmitter is activated. Upon signal from the AND gate 33, the switch 34 is opened and the transmitter is deactivated. The elements in the receiver part that require drive voltage are always connected to the drive source and the receiver is constantly activated. The last section 30 of the shift register 25 is connected to the control input of the transmitter 16 via a converter 37 which converts the channel number in the register 25 to a suitable control voltage for the transmitter. 455 890 The function is as follows.

When a listening device is to be activated, the master station sends a pulse train, the first part, which ends up in section 27, contains the ID number of the current listening device, and whose second part, which ends up in section 28, represents activation orders and finally a pulse train. which ends up in section 30 and represents the selected channel. The transmitter is activated and any sound picked up by the hydrophone is transmitted in the selected channel. Every ten seconds, the transmission of the audio information is interrupted and instead ID information from the memory 17 is sent out in the special channel. During this ID transfer, position determination of the current interception device takes place. This continues until the master station eats out transmits the ID number of the device in question together with a signal which ends up in section 29 of the register 25, whereby the transmitter is deactivated.

Figure 3 schematically shows the signal processing part of the M1 receiver of the master station, which relates to the determination of the position of a sound source relative to three selected listening devices. If the channels are frequency channels, ie a special carrier or subcarrier frequency for each channel, the receiver part in principle consists of a number of bandpass filters tuned to their respective frequencies, in the case of subcarriers preceded by a filtering and mixing step for suppressing the main carrier, wherein 3 shows the receiver channels for the three selected listening devices represented by the bandpass filters F1, FZ and F3 with associated detectors D1, D2 and D3. The detectors are connected to their respective outputs 01, 02 and 03 where the low-frequency modulation signal in each channel appears. At the outputs 01, 02 and 03, the same sound information thus appears, but in different time modes depending on different running times for the sound in the water to the respective listening device. (This disregards the differences in running time for the radio waves in the air). The signal processing is in principle such that the audio signals are correlated in pairs to determine their mutual time difference. Thus, in Fig. 3, the signals at the outputs 01 and 02 are connected via a switching network SW to a first correlator K1, while the signals at the outputs 01 and 03 via the SW are routed to a second correlator K2. The correlator K1 gives the time difference T1 and the correlator K2 gives the time difference T2. The time differences T1 and T2 each represent a hyperbola and the sound source U is at the intersection of these hyperbells. Fig. 4 schematically shows how the position of the various listening devices can be determined in the master station by specifying the components required for locating the first listening device A1 (Fig. 1). The location of the listening devices takes place as mentioned during the short interruptions in the sound transmission 455 890 Kb, when ID information is transmitted in a special channel. It is assumed that the device A1 is alone in transmitting ID information at a certain time. This information is transmitted as a zero train in the given channel, ie on a given channel frequency, and is relayed further by the selected relational relations M2 and M3 in two other channels. To separate these signals, the master station contains three bandpass filters, a filter F4 which is tuned to the channel frequency used by the interceptor A1 (and also other interceptors) for transmitting ID information, and two filters F5 and F6 tuned to the channel frequencies. to which said frequency is converted in the relay station M2 resp. M3.

The filters F4, F5 and F6 are connected via their respective detectors D4, 05, D6 to their respective outputs 04, 05, 06. At these outputs, one and the same ID information thus appears, namely the ID address of the interception device A1, but in different time modes. The signal processing for determining the position of the device A1 is in principle such that the ID signal on said outputs is compared two and two after correction for the known running times from M2 to M1 resp. from M3 to M1 to determine their mutual time difference when they arrive at the respective stations M1, M2 and M3. Thus, the signal at the first output 04 is connected to a first input of a comparator J1 via a time delay circuit B1, the signal delays the known running time Z / 1 from M2 to M1, while the signal of 05 is routed directly to a second input of the comparator J1. Correspondingly, the signal at output 04 is connected to a first input of a second comparator J2 via a time delay circuit B2 which delays the signal the known running time 212 from M3 to M1, while the signal at output 06 is connected directly to a second input of J2. The comparator J1 gives a time difference T3 as output signal and J2 gives a time difference T4. The time differences T3 and T4 each represent a hyperbola and A1 is at the intersection of these hyperbells. The time differences T3 and T4 or possibly the calculated position are stored together with the ID number of the device A1.

At different subsequent times, the same information comes from A2 and A3 which are located in the same way and with the same circuits. Every ten seconds, the ID number returns from A1 and the stored information about the position of the device is constantly updated.

The function of the entire plant is as follows.

After placing the interception devices in a water area with a suspected sound source and setting up the fixed stations M1, M2 and M3, a general information collection phase begins which is to determine whether there are certain indications of a sound source within the monitored area and 10 455 890 in if so, its approximate location. This information collection phase can, for example, mean that the interception devices are called and activated in turn. As soon as a listening device is activated, it transmits the recorded sound and its ID number, whereby the position of the station can be determined. ID number, mode and a rough information about recorded sound are stored. It now turns out that a number of nearby listening devices have a sound exceeding a certain level and of a similar nature, only these listening devices are activated and measurement of the sound source takes place in the described manner.

In order to optimize the transmission in relation to the required bandwidth, the audio signal can be digitized and channel separation can be achieved by time division multiplexing.

Fig. 5 shows a simplified block diagram of a listening device operating according to this principle. The interception devices (buoys) are assumed to cooperate with a number of fixed radio stations, one of which, the master station, has an accurate clock and sends out synchronization or jerking pulse to all buoys and activation orders to certain selected buoys. Each buoy has a receiver 100 and a transmitter 101. Via two switches 102, 103, which normally assume the position shown, the receiver 100 is connected to an antenna 104. Via the same switch, the transmitter 101 can be connected briefly to the antenna 104. To the output of the receiver 100 three detectors are connected, an ID detector 105, a channel detector 106 and a synchronization or jerking detector 107. The synchronization detector 107 controls a clock 108 whose output signal together with the output signal from the channel detector 106 controls a channel selection circuit 109. A memory 110 is continuously charged with samples of the audio signal which is picked up by a hydrophone 111 and which samples are generated by means of an amplifier 112 and an AD converter 113. The information in the memory 110 is led via a reading device 114 to the input of the transmitter 101. The memory 110 is reset by means of a signal from the jerk detector 107, while the reading device 114 is activated from the channel selection circuit 109. This circuit also controls the switch 103, while the switch 102 is controlled by means of a signal from the ID detector 105.

The function is as follows.

With regular time intervals, e.g. of the order of 0.1-10 sec., the sync pulse or jerking pulse comes and resets the clocks in all buoys.

These watches can therefore be moderately accurate and of cheap design. With these assumed large time intervals, the difference in the running time of the sync pulse to different buoys becomes negligible and the clocks can be assumed to run the same. At the same time, the memory, which has such a capacity that it holds all the samples that represent the audio signal in the entire time interval between two sync pulses, is reset. This time interval between 45 sync pulses is divided into a number of sub-intervals, e.g. ten pieces each representing a channel and for example with a length of 0.01-1 sec. Each such sub-interval is assigned a channel number 1, 2, .... 10. When the master station now wants a certain buoy to transmit its recorded sound, the buoy's ID number is first transmitted immediately followed by a signal representing activation orders. The 10-detector 135 in the current buoy reacts and sets the switch 102 to the position shown. The buoy is now activated for transmission.

Immediately thereafter, the master station transmits a pulse sequence representing the channel number to be assigned to the buoy. This pulse sequence is detected by the channel detector 106, which controls the channel selection circuit 109. In response, the output circuit 109 outputs a number of sub-intervals equal to the channel number after the sync pulse. The signal from the circuit 109 adjusts the switch 103 to the position not shown and initiates the reading device 114. When the reading device 114 receives a control signal, the memory 110 is read at a high speed and the sampled audio signal is transmitted via the antenna 104 in compressed form by modulation here in the current wave. the time channel. The same thing is then repeated for another buoy and another channel. In the master station and other fixed stations, the connection between channel / ID number is stored. Here, therefore, the memory packets representing the sound signals picked up by the different buoys can be shifted in time, taking into account the time position of the different channels, and the correlation can be executed in the manner previously described. Optionally, additional shifts can be made to correct for time errors that have occurred due to the different running time of the sync pulse to different buoys.

Instead of selective individual activation, as in the described exemplary embodiments, it is alternatively possible to activate the interception devices in groups, e.g. depending on their geographical location, as described in SE B 435 978.

If fixed listening devices are located in the vicinity of an area to be monitored, it is also possible to use these devices in combination with one or more of the free-floating buoys provided with radio transmitters.

Claims (8)

1,455,890 ß Patent claim. l. A method of determining the position of a sound source within a water area by recording sound emitted from the sound source with at least three listening devices each comprising a hydrophone which cooperates with radio transmitters for transmitting recorded sound on radio carrier to an evaluation unit, characterized by that at least one listening device with an unknown position in the water area, suitably on a free-floating buoy, and that the position of the sound source is determined in two steps by 1) first determining the position of said listening device with an unknown position, which takes place by time correlation between signals transmitted on carrier from the listening device to three receivers with known position, and position determination using the running time of the radio waves and that 2) the position of the sound source relative to the three listening devices is determined by time correlation between signals representing sound waves from the sound source received by the three interception devices, and posit determination using the travel time of the sound waves to the three listening devices. 2. A method according to claim 1, characterized in that both the signal used for determining the position of the listening device (s) as well as the position of the sound source relative to the listening devices represent sounds recorded by the respective listening device. 3. A method according to claim 1, characterized in that the position determination of the interceptor device (s) having an unknown position takes place with the aid of time correlation between a characteristic signal transmitted from the respective interceptor device at short intervals in the intermittent position. goat sound modulated carrier. Oh. 4. A method according to claim 3, characterized in that the characteristic signal contains for each eavesdropping device individual identification information, so-called ID information. - An installation for carrying out the method according to any one of claims equal to determining the position of a sound source in a water area by means of at least three listening devices comprising hydrophones, which cooperate with radio transmitters for transmitting recorded sound on a carrier to an evaluation unit, -f / 4 *. 455 890 characterized in that a number of interceptors are spread over an unknown position within the water area, suitably mounted on free-floating buoys, that each interceptor in addition to the hydrophone and transmitter is also provided with receivers for selective control by supplied control information. and that the system includes at least three radio stations with known positions with receiving means for receiving modulated signals from selected listening devices, and there is also first correlator means for comparing the time state of a signal from a selected listening device received in the three radio stations and other correlating means for comparing the time state of a signal representing sound emitted from the sound source emitted by at least three selected listening devices, and evaluation means for determining the position of each selected listening device by means of the output signal from said first correlator means using the running time of the radio waves from respect ive listening device to the three radio stations and determining the position of the sound source relative to the selected listening devices by means of the output signal from said second correlator means using the travel time of the sound waves from the sound source to the selected listening devices. Plant according to claim 5, characterized in that the intercepting devices are designed to transmit a characteristic signal intermittently during short interruptions in the recorded modulated carrier, the position determination of the intercepting devices taking place by time correlation between said characteristic signal when it is received in the three radio stations with known positions. Plant according to claim 6, characterized in that the characteristic signal contains for each eavesdropping device individual identification information, so-called ID information. Plant according to one of Claims S-7, characterized in that at least two of the radio stations with known position are relay stations which relay the modulated signal from each selected listening device to a master station, where time correlation between the different signals from one and the same listening device takes place with knowledge of the known gangways from the respective relay station to the master station.